{"id":"CVE-2026-25541","aliases":["RUSTSEC-2026-0007","GHSA-434x-w66g-qw3r"],"title":"Integer overflow in `BytesMut::reserve`","summary":"Integer overflow in `BytesMut::reserve`","severity":"none","vendor":"bytes","product":"bytes","ecosystem":"rust","affected":["bytes >= 1.2.1, < 1.11.1"],"patched":["bytes 1.11.1"],"published":"2026-02-03","updated":"2026-10-12","sourceUpdated":"2026-10-12T18:00:09.239418978Z","source":"OSV","sourceUrl":"https://osv.dev/vulnerability/RUSTSEC-2026-0007","references":[{"url":"https://crates.io/crates/bytes"},{"url":"https://rustsec.org/advisories/RUSTSEC-2026-0007.html"},{"url":"https://github.com/tokio-rs/bytes/commit/d0293b0e35838123c51ca5dfdf468ecafee4398f"}],"tags":["osv","rust","exploit-available"],"epss":0.0061,"epssPercentile":0.47735,"exploits":{"github":1,"githubRepos":["https://github.com/trajanOx/cve-2026-25541-fuel-analysis"],"checkedAt":"2026-10-13T11:46:04.385Z"},"exploitAvailable":true,"ingestedAt":"2026-10-13T11:45:30.183Z","slug":"CVE-2026-25541","body":"## Overview\n\nIn the unique reclaim path of `BytesMut::reserve`, the condition\n```rs\nif v_capacity >= new_cap + offset\n```\nuses an unchecked addition. When `new_cap + offset` overflows `usize` in release builds, this condition may incorrectly pass, causing `self.cap` to be set to a value that exceeds the actual allocated capacity. Subsequent APIs such as `spare_capacity_mut()` then trust this corrupted `cap` value and may create out-of-bounds slices, leading to UB.\n\nThis behavior is observable in release builds (integer overflow wraps), whereas debug builds panic due to overflow checks.\n\n## PoC\n\n```rs\nuse bytes::*;\n\nfn main() {\n    let mut a = BytesMut::from(&b\"hello world\"[..]);\n    let mut b = a.split_off(5);\n\n    // Ensure b becomes the unique owner of the backing storage\n    drop(a);\n\n    // Trigger overflow in new_cap + offset inside reserve\n    b.reserve(usize::MAX - 6);\n\n    // This call relies on the corrupted cap and may cause UB & HBO\n    b.put_u8(b'h');\n}\n```\n\n# Workarounds\n\nUsers of `BytesMut::reserve` are only affected if integer overflow checks are configured to wrap. When integer overflow is configured to panic, this issue does not apply.\n\n## Affected packages\n\n- `bytes >= 1.2.1, < 1.11.1`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `bytes 1.11.1`","depth":"twilight","depthScore":15,"depthScoreParts":{"impact":2.8,"likelihood":0.1,"exploitation":12,"ransomware":0},"changes":[]}